The present invention relates to the field of semiconductor manufacturing, and more particularly, to the formation of strained device film for silicon-on-insulator (SOI) devices.
The advantages of silicon-on-insulator (SOI) technology for complementary metal-oxide-semiconductor (CMOS) integrated circuits (ICs) are well documented. Typically, SOI technology reduces undesired p-n junction capacitance between source/drain and a substrate by approximately 25% as compared to other conventional techniques for CMOS ICs. Furthermore, CMOS ICs fabricated with SOI technology have less active current consumption while maintaining device performance equivalent to that of similar devices formed on bulk-silicon substrates. Other advantages of SOI technology include suppression of the short channel effect, suppression of the body-effect, high punch-through immunity, and reduced latch-up and soft errors. As the demand increases for battery-operated equipment, SOI technology is becoming increasingly more popular due to the low power requirements at high speeds of SOI devices.
There are many different techniques for formation of SOI wafers. These include SIMOX, which is separation by implanted oxygen technology. Wafer bonding is another technique for forming an isolation layer in a substrate. Forming silicon islands through a series of etch and oxidation steps can provide lateral isolation structure.
In standard MOSFET technology, the channel length and gate dielectric thickness are reduced to improve current drive and switching performance. Carrier mobility of a MOSFET device is an important parameter because of its direct influence on output current and switching performance. Accordingly, another way to increase device performance is to enhance the channel mobility. This enhancement has been provided in certain devices by straining the silicon film. A net strain can be provided by compressive stress of the silicon film, or tensile stress of the silicon film.
It is desirable to provide the isolation advantages of SOI technology and silicon islands, yet also provide the improved device performance achieved through enhancement of carrier mobility.
There is a need for providing a strained silicon film in an SOI device having silicon islands to increase the device performance by enhancing the carrier mobility in the silicon film.
This and other needs are met by embodiments of the present invention which provide a method of forming strained device film comprising the steps of etching recesses in a buried oxide layer of a silicon-on-insulator (SOI) structure having a substrate, a buried oxide layer on the substrate, and a silicon layer on the buried oxide layer. The silicon layer has trenches, and the etching of recesses in the buried oxide layer include etching through the trenches in the silicon layer. The recesses in the buried oxide layer and the trenches are filled with a material that induces a net amount of strain in the silicon layer.
By replacing some of the buried oxide layer with other material, a net amount of strain in the silicon layer may be induced to provide a desired amount of and type of stress. For example, in certain embodiments, nitride is deposited into the recesses and the buried oxide layer and the trenches in the silicon layer. Changing the material will change the amount and type of stress, such as either tensile or compressive stress, that produces the net amount of strain in the silicon layer. Hence, the present invention improves the device performance by enhancing the channel mobility in the SOI devices that are created.
The earlier stated needs are also met by embodiments of the present invention which provide a silicon-on-insulator (SOI) device with strained silicon film, comprising a substrate and a buried oxide layer on the substrate. Silicon islands are provided on the buried oxide layer. The silicon islands are separated from each other by gaps. The buried oxide layer has recesses directly under the gaps. A material fills the recesses and the gaps, this material inducing a net amount of strain in the silicon islands.
The foregoing and other features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.